Northern wild-rice (manoomin) is limited by a warm lake and the co-occurrence of native and non-native aquatic plants in Northern Michigan, USA

Introduction Zizania palustris (northern wild-rice, manoomin), is foundational to the cultural heritage of indigenous peoples in the Great Lakes region of North America, provides habitat for diverse fauna, and its regional distribution and abundance have been substantially reduced. Restoration and sustainable stewardship of manoomin is a shared goal of tribes across the region. Methods Our research objective was to refine our understanding of manoomin’s ecological niche and competitive dynamics in order to improve restoration outcomes through four related studies: Study one (Q1) evaluated differences between lakes with differing seeding successes; study two (Q2), quantified manoomin growth and environmental conditions within mixed aquatic plant communities; study three (Q3) tested experimental manoomin seeding within three dominant aquatic plant types; and study four (Q4) evaluated the indirect effects of shading and invasive plant ( Typha × glauca ) litter on manoomin. Results We found that the warmer of two lakes sampled had dramatically lower manoomin productivity (Q1); Pontederia cordata was negatively associated with manoomin (Q2); manoomin was more abundant and larger in Nuphar variegata stands (Q3); and litter from T. × glauca and a proxy for floating plant cover reduced germination and early growth (Q4). Discussion Our findings illustrate that both native and invasive plants can be detrimental to the germination, growth, and productivity of manoomin. T. × glauca and its litter caused particularly strong negative effects, indicating that invasive plant management is necessary for sustainable restoration. Our study points toward areas for future manoomin research and highlights the multifaceted threats of global change factors (e.g., climate change and non-native macrophytes) on plant species of high cultural importance.